Genetics clearly contributes to individual risk for nicotine dependence in humans and variations in nicotine sensitivity in experimental animals. In mice, several behavioral and physiological responses to nicotine have been demonstrated to be influenced by genetics. However, none of the specific genes that contribute to the genetic influence on nicotine sensitivity in mice have been identified. These genes remain an untapped source of information that almost certainly will improve our understanding of what drives individual differences in nicotine sensitivity. For example, the recent discovery that variants in human CHRNA5 are associated with risk for nicotine dependence in humans led to follow-up studies in rodents which not only helped to identify a specific neuronal pathway critical for controlling the level of nicotine consumption, but also demonstrated that this gene impacts individual differences in nicotine self-administration not by increased sensitivity to the reinforcng effects of nicotine at low doses but rather a lack of the loss of reinforcement at aversive doses. This is just one of many examples where the identification of a gene that contributes to individual variability in a phenotypic measure can lead to significant insights into the underlying biology of the measure. We previously have mapped chromosomal regions that harbor genes or genes that contribute to individual differences in oral nicotine intake in mice and it is the goal f this project to follow up this initial finding to identify the genes that contribute to variation i nicotine intake. For this, we will again map chromosomal regions that impact nicotine intake but this time in a panel of mice that will allow us to define with much greater precision the regions i the genome that harbor genes that impact nicotine intake. We will follow this up with selective breeding to produce lines of mice that differ in nicotine intake. The selection process should produce mouse lines that are enriched for alleles that are involved in increasing or decreasing nicotine intake. Finally, we will perform whole genome sequencing on the selected lines. We will use these sequencing data to establish whether the chromosomal regions identified through mapping are enriched through the selection process and to identify all variants within the region. We also will analyze the sequence data for other potential chromosomal regions that have been enriched through selection for nicotine consumption. This multi-tiered approach should allow us to substantially narrow the search for variants that influence nicotine intake and potentially lead to the identification of causal variants (functional variants that contribute to individual variabiity in nicotine consumption).